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Cannot open display

The Cannot open display error is one of the most frequently seen errors with using X11 Client applications.

Note that this page may be helpful for all X Servers, but the support provided here was created for StarNet’s X Server, X-Win32.

There are two major causes of this error:

  1. X-Win32 7.1 and earlier could pass the wrong display address to the remote machine when you had multiple network cards (e.g. wired and wireless); X-Win32 8 has been enhanced to automatically select the correct network address; thus, if you are having this problem, please consider upgrading to X-Win32 8 today!
  1. Alternatively, this may not be a problem with X-Win32 or your X Server. Rather, this error can be an indicatation that your X11 Client application cannot find a network path (or the path is blocked by a firewall) to X-Win32.

    We have created troubleshooting steps that are specific to your connection type (e.g. rexec, rsh, Xdmcp, etc.). Follow the links below for these detailed troubleshooting steps:

  • Session ends with “Cannot Open Display” error

    Diagnosis

    There is probably not a direct path from your Windows system to the host you’re trying to reach. First, try to ping your host (by hostname or IP address) and make sure you can reach it. If that works and if you have full access to all systems and routers between the X-Win32 system and the host, then you should be able to get X-Win32 working.

    Suggestions

  • First, make sure you are using the wizard to create the session (under Xconfig, Sessions). The wizard will automatically setup your $DISPLAY variable which will prevent the cannot open display issue. Make sure there is no reference to $DISPLAY in the users’ .profile, .cshrc file, or any startup files. This will override the $DISPLAY settings set by the X-Win32 wizard and will cause the cannot open display issue. To test against this, make a new user on the host system and try connecting to the host via X-Win32 and the new user name. If you can connect with the new user, there’s an issue with one of the users’ startup files.
  • If you have another X-Win32 system available, try using that to connect to your host. If it works, then the problem is limited to something on the Windows side of the original system which cannot connect.
  • If you aren’t sure how to setup security under Xconfig, Security, do not make changes to this tab. Changing security settings could make the X-Win32 reject all session requests. If you made changes to this tab, uncheck everything and make sure nothing is listed in the xhost list. Press okay, this will restore default security settings.
  • Try removing all routers and firewalls between the X-Win32 system and the host and see if that helps. Disable ZeroAlarmPro, Norton, McAfee, any security programs which might be blocking the connection. If X-Win32 now can connect, add back each firewall, one at a time, properly configuring it and testing X-Win32 to make sure X-Win32 can connect through the firewall. Firewalls need ports 6000-6010 TCP open in both directions as well as port 177 UDP open in both directions.
  • Sometimes in an DHCP network, if the system admin hasn’t properly setup hostname and IP address association, this can cause cannot open display. When you invoke a remote connection, usually the host does a reverse DNS lookup to make sure the system requesting the session is a legitimate system on the network. If the host does a reverse DNS lookup and sees multiple DNS entries for your X-Win32 system, it will send cannot open display because you are failing the reverse DNS lookup. The quick solution is to add the Windows X-Win32 system’s hostname and IP address to the /etc/hosts file on the host you’re trying to connect to.
  • If you receive the message, “Where are you?” this is similar to the above issue. The quick solution is to add the Windows X-Win32 system’s hostname and IP address to the /etc/hosts file on the host you’re trying to connect to.
  • If you have VPN client software installed, be sure it doesn’t have an active firewall. Some VPN clients like the Cisco VPN client has a built in firewall which is active even if the Cisco VPN isn’t active. If you can’t disable the firewall, open ports 6000-6010 TCP open in both directions as well as port 177 UDP open in both directions.
  • Some systems like laptops have multiple network connectors. Make sure under Xconfig, Display that the appropriate IP address is selected. If you connect to the host via a wireless adapter, make sure the wireless adapters’ IP address is selected under Xconfig, Display. If you’re connecting from home and behind a router, you’ll need to use IPsmart or figure out your routers’ global IP address.

    Xdmcp Connections

    Symptoms

  • Session won’t connect with no error
  • Session ends with “Cannot Open Display” error
  • X-Win32 displays only a black and gray crosshatch screen

    Diagnosis

    There is probably not a direct path from your Windows system to the host you’re trying to reach. First, try to ping your host (by hostname or IP address) and make sure you can reach it. If that works and if you have full access to all systems and routers between the X-Win32 system and the host, then you should be able to get X-Win32 working.

    Suggestions

  • First, make sure you are using the wizard to create the session (under Xconfig, Sessions). The wizard will automatically setup your $DISPLAY variable which will prevent the cannot open display issue. Make sure there is no reference to $DISPLAY in the users’ .profile, .cshrc file, or any startup files. This will override the $DISPLAY settings set by the X-Win32 wizard and will cause the cannot open display issue. To test against this, make a new user on the host system and try connecting to the host via X-Win32 and the new user name. If you can connect with the new user, there’s an issue with one of the users’ startup files.
  • If you have another X-Win32 system available, try using that to connect to your host. If it works, then the problem is limited to something on the Windows side of the original system which cannot connect.
  • If you aren’t sure how to setup security under Xconfig, Security, do not make changes to this tab. Changing security settings could make the X-Win32 reject all session requests. If you made changes to this tab, uncheck everything and make sure nothing is listed in the xhost list. Press okay, this will restore default security settings.
  • Sometimes in an DHCP network, if the system admin hasn’t properly setup hostname and IP address association, this can cause cannot open display. When you invoke a remote connection, usually the host does a reverse DNS lookup to make sure the system requesting the session is a legitimate system on the network. If the host does a reverse DNS lookup and sees multiple DNS entries for your X-Win32 system, it will send cannot open display because you are failing the reverse DNS lookup. The quick solution is to add the Windows X-Win32 system’s hostname and IP address to the /etc/hosts file on the host you’re trying to connect to.
  • If you receive the message, “Where are you?” this is similar to the above issue. The quick solution is to add the Windows X-Win32 system’s hostname and IP address to the /etc/hosts file on the host you’re trying to connect to.
  • If you have VPN client software installed, be sure it doesn’t have an active firewall. Some VPN clients like the Cisco VPN client has a built in firewall which is active even if the Cisco VPN isn’t active. If you can’t disable the firewall, open ports 6000-6010 TCP open in both directions as well as port 177 UDP open in both directions.
  • Some systems like laptops have multiple network connectors. Make sure under Xconfig, Display that the appropriate IP address is selected. If you connect to the host via a wireless adapter, make sure the wireless adapters’ IP address is selected under Xconfig, Display. If you’re connecting from home and behind a router, you’ll need to use IPsmart or figure out your routers’ global IP address.
  • Check to be sure the XDM process is running on your host. On a Linux or Solaris host, run, “netstat –an | grep 177” and see if your host has a socket open listening. If it doesn’t, check to be sure XDM is running on the host. Here are some typical responses from a properly configured host:
    Sun Microsystems Inc. SunOS 5.10 Generic January 2005
    $ netstat -an | grep 177

    *.177 Idle

    *.177 Idle
    Observe the 2 processes listening on port 177 for XDM connections. On a Solaris system, dtlogin is the process that listens for XDM requests. You can also observe this checking for the dtlogin process (Solaris only):

    $ ps -u root | grep dtlogin
    448 ? 0:00 dtlogin
    396 ? 0:00 dtlogin
    $
    You can see dtlogin is running and you can see the host is listening on port 177 for XDMCP connections. If you don’t observe XDM running, ask your system administrator why the host isn’t listening on port 177 for remote connections.

  • Try removing all routers and firewalls between the X-Win32 system and the host and see if that helps. Disable ZeroAlarmPro, Norton, McAfee, any security programs which might be blocking the connection. If X-Win32 now can connect, add back each firewall, one at a time, properly configuring it and testing X-Win32 to make sure X-Win32 can connect through the firewall. Firewalls need ports 6000-6010 TCP open in both directions as well as port 177 UDP open in both directions. If using Gnome 2.0, port 16001 TCP needs to be open as well in both directions.

    Using an External Tool (such as PuTTY or telnet)

    Symptoms

  • Invoking an Xwindow results in Session won’t connect with error, “X connection to localhost:10.0 broken (explicit kill or server shutdown).”
  • Session ends with “Cannot Open Display” error
  • Xwindow process starts but never displays

    Diagnosis

    There is probably not a direct path for X-Win32 traffic from your Windows system to the host you’re trying to reach. First, try to ping your host (by hostname or IP address) and make sure you can reach it. If that works and if you have full access to all systems and routers between the X-Win32 system and the host, then you should be able to get X-Win32 working. When connecting passively, remember that:

  • The telnet or PuTTY client needs the correct value for $DISPLAY so the host can send the session back to the correct IP address.
  • Ports 6000-6010 TCP as well as port 177 UDP need to be open in both directions for all routers and firewalls between X-Win32 and the host.

    Suggestions

  • First, once you are connected to your host via PuTTY, telnet or any 3rd party client, run, “echo $DISPLAY” to see what the $DISPLAY variable is. It should be either your local system’s IP address, or it should be the global IP address of the router you are behind. If you are using Ssh with X11 forwarding, this will echo “localhost:10.0” or something similar. Using Ssh with X11 forwarding is the easiest method to tunnel your display to X-Win32. The “localhost:10.0” means the Ssh client will forward X11 traffic over Ssh which X-Win32 can then create Xwindows with.
  • If you have another X-Win32 system available, try using that to connect to your host. If it works, then the problem is limited to something on the Windows side of the original system which cannot connect.
  • Make sure X-win32 is running. You should see a dark blue “X” near the system clock.
  • If you aren’t sure how to setup security under Xconfig, Security, do not make changes to this tab. Changing security settings could make the X-Win32 reject all session requests. If you made changes to this tab, uncheck everything and make sure nothing is listed in the xhost list. Press okay, this will restore default security settings.
  • Try removing all routers and firewalls between the X-Win32 system and the host and see if that helps. Disable ZoneAlarm Pro, Norton, McAfee, any security programs which might be blocking the connection. If X-Win32 now can connect, add back each firewall, one at a time, properly configuring it and testing X-Win32 to make sure X-Win32 can connect through the firewall. Firewalls need ports 6000-6010 TCP open in both directions as well as port 177 UDP open in both directions.
  • If you have VPN client software installed, be sure it doesn’t have an active firewall. Some VPN clients like the Cisco VPN client has a built in firewall which is active even if the Cisco VPN isn’t active. If you can’t disable the firewall, open ports 6000-6010 TCP open in both directions as well as port 177 UDP open in both directions.

    Category:Errors
    Category:Sessions -> rexec
    Category:Sessions -> rsh



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